Multiaxial pin seamed papermaker&#39;s press felt

ABSTRACT

A multilayer papermaker&#39;s press felt fabric comprising in combination a woven first fabric layer, typically a double layer fabric, has a cross machine direction pin seam. A second fabric layer is located on the paper side face of the first fabric layer, and a layer of needled batt is applied to the paper side face of the second layer binding the layers together. A flap comprising a short length of the second fabric layer with attached batt overlays the pin seam area in the first layer. The second layer comprises a plurality of relatively narrow strips, which are located with a lateral edge at a first cant angle of from more than 1° to less than 20° to the machine direction. A third layer, similar to the second layer, can be included on the machine side of the first layer; the strip widths, the cant angles, and the direction of the cant angle relative to the machine direction for each of the two strips need not be the same. The fabric is assembled using a spiral winding technique.

This application is a cip of U.S. Pat. No. 08/805,202 filed Feb. 27,1997, now abandoned.

BACKGROUND TO THE INVENTION

This invention relates to press felts, which are used in the presssection of a paper making machine. In this part of the papermakingmachine, the paper web, which may contain up to about 85% water, ispassed between pairs of opposed rolls so that a large proportion of thiswater is literally squeezed out of the wet paper web. In this process,the wet paper web is supported by at least one, or conveyed between twoopposed fabrics known as press felts. These press felts are generallyconstructed with a fabric base structure, which has layers of battneedled to at least one, and generally to both, of its surfaces. Severalfabric constructions are used for the base fabric structure, includingboth single layer and double layer woven fabrics, and the fabrics can bewoven either flat as a continuous run, or endless as a closed loop.Endless felts require that the press section be opened up to allow theirinstallation. Seamed felts are open ended for installation and the endsare subsequently joined by seaming, for example with a pin seam, on thepress section. In either case, in order to be able to install thefinished fabric into a press section, it is often advantageous to makeprovision for a seam that can be closed during installation in the presssection.

The seam is the most difficult part of the press fabric to make. Foralthough it is relatively straight forward to create a press felt whichwill provide the required properties of adequate strength, adequatedrainage, and lack of fabric marking, whether or not it can be useddepends upon also being able to provide a seam in the fabric which hasan adequate life in service, provides the required strength, providesthe required drainage, and most importantly does not cause marking ofthe paper.

The most commonly used seam in press felts is a pin seam, in whichmonofilament yarns from each of the two ends of the fabric which are tobe joined are woven back into the fabric ends to provide a set of smallloops. The two fabric ends are joined by interdigitating the two sets ofloops, and inserting a pintle across the width of the fabric. This formof seam is most often used in press felts based on double layer wovenfabrics. Examples of such seams are shown in EP 0 294 951, U.S. Pat. No.4,842,925 and U.S. Pat. No. 4,601,785.

These conventional press felts offer the benefits of ease ofinstallation, and ease of seam assembly on the machine. But they havethe disadvantages of being limited to applications which can tolerate atleast some marking of the paper by the seam, and where the drainagerequirements are modest. A further disadvantage is that the applied battwears more rapidly in the seam area. An area of worn batt cover over theseam area increases the danger of marking, and also accelerates evenmore the rate of wear in the seam area. This leads to premature pressfelt failure due to either paper marking problems, or mechanical seamfailure, or both.

Several proposals have been made to overcome these difficulties.

One that has been made is to use two woven fabric layers, rather thanone, to provide what may be termed a laminated base structure. Fabricsof this type are shown in U.S. Pat. No. 3,086,276, wherein the fabriclayers are disposed in a bias relationship, and in U.S. Pat. No.3,657,068 in which a relatively fine and a relatively coarse fabric aredisposed on each side of a layer of batt. An alternative fabric is shownin U.S. Pat. No. 5,110,672. In these references, the layers arelaminated together by the batt which in the needling application processis forced into engagement with all of the layers. A problem common toall of these structures is that the cut fabric ends adjacent the seamtend to unravel, thus leaving the batt more or less unsupported in themost important area of the fabric. This leads to marking of the paper,and to premature seam failure.

Alternatively, it has been proposed to use a laminate structure,examples of which are described in U.S. Pat. No. 4,186780 and in U.S.Pat. No. 4,418,726, and to pin seam each of the fabrics in the laminate.Apart from the fact that this does not eliminate any of the difficultiesattendant on a single pin seam, it further complicates installation, asthere are now two seams to be closed, not one. Such an installation stepis difficult, time consuming and defeats the original purpose of theseam, which is to provide ease of installation.

Another proposal is to provide what may be termed a “flap” of batt,which may be reinforced with a portion of the fabric base, that willoverlay a conventional pin seam, preferably on the paper side of thefabric. Examples of this are described in CA 1,303,833 and EP 0 294 951mentioned above. In each of these, in constructing the pin seam, a shortflap of batt is provided which is attached to one of the ends to bejoined and which is intended to cover the joint after the pin seam hasbeen assembled. In U.S. Pat. No. 4,601,785 it is recommended to attachthe batt flap by gluing or needling. In U.S. Pat. No. 4,842,925 it isrecommended to use brittle or soluble yarns adjacent the seam. Eitherduring or following the needling step to attach the batt these yarns areremoved thus allowing the batt flap to be cut and placed in position. InEP 0 294 951 it is recommended to use an additional layer of machinedirection yarns in the base fabric to reinforce the batt flap. Seamssuch as these are also difficult to assemble, and suffer from thedisadvantage that the fabric in the flap supporting the batt also endsto unravel, thus leaving the batt unsupported which results in markingof the paper.

SUMMARY OF THE INVENTION

This invention seeks to provide an alternative solution to theseproblems. A press felt is provided in which a laminate fabric is used asthe base fabric, only the first layer of which is joined end-to-end by apin seam. The second layer is cut to provide a batt carrying flap overthe pin seam. The second layer is also canted with respect to the firstlayer, so that the cut seam is at an angle with respect particularly tothe fabric wefts, thus inhibiting the loss of these yarns due to thefabric unravelling. The second fabric is also made in relatively narrowstrips, thus further diminishing the possibilities of unravelling.

Thus in a first embodiment this invention seeks to provide a multilayerpapermaker's press felt fabric comprising in combination:

-   -   a woven first fabric layer incorporating therein a cross machine        direction pin seam,    -   a second fabric layer on the paper side face of the first fabric        layer,    -   a layer of needled batt applied to the paper side face of the        second layer which penetrates into the first fabric layer        thereby binding the first and second layer together, and    -   a flap comprising a short length of the second fabric layer with        attached batt overlaying the pin seam in the first layer,        wherein:        -   (a) the second layer comprises a plurality of relatively            narrow strips, and        -   (b) the strips of the second layer are located with a            lateral edge at a first cant angle to the machine direction,            and        -   (c) the first cant angle has a value of from more than 1° to            less than 20°.

In a second the fabric further includes a third layer on the machineside of the first layer wherein:

-   -   -   (a) the third layer comprises a plurality of relatively            narrow strips, and        -   (b) the strips of the third layer are located with a lateral            edge at a second cant angle to the machine direction, and        -   (c) the second cast angle has a value of from more than 1°            to less than 20°.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in one embodiment by way ofreference to the drawings, in which:

FIG. 1 is a section perpendicular to the plane of a press felt through apin seam,

FIG. 2 is a partly sectioned paper side view of a press felt, and

FIG. 3 is a partly sectioned paper side view of an alternative pressfelt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this invention the following terms are of importance:

-   -   “machine direction” refers to a direction taken along the length        of the press section, which is substantially parallel to the        direction in which the press felt moves, and the associated term        “cross machine direction” refers to a direction substantially at        a right angle to the machine direction;    -   “paper side” refers to the side of a press felt, or of the basic        woven structure, that is towards the paper when the press felt        is installed, and the related term “machine side” refers to the        side of the press felt, or of the basic woven structure, that is        toward the press section rolls when the press felt is installed;        and    -   “cant angle” refers to an angle between a lateral edge of a        fabric forming part of the basic woven structure and the machine        direction.

Referring first to FIG. 1, the part section shown is taken along themachine direction. The press felt shown generally at 1 is composed ofessentially three layers, to which a fourth can be added, and whichincludes a seam as shown generally at 2. The supporting base fabriccomprises a first machine side fabric 3 which includes the seam 2.Overlaying the paper side of this first layer 3 is a second layer 4;these layers are held together by the applied batt 5 which penetratesthrough the second layer 4 to some extent into the first layer 3. Ifdesired, a further layer of batt can be applied to the machine side ofthe first layer 2 as shown ghosted at 6. The first layer, which as shownis a relatively simple double layer weave, that includes wefts 7 in thecross machine direction, and warps 8 and 11 in the machine direction.The pin seam is formed by weaving back lengths of the warps 8 and 11respectively to provide the loops 9 and 12 respectively. The seam isheld together by the pintle 10 inserted into the loops 9 and 11. Thisform of seam construction is well known.

The upper second fabric on the paper side of the first is a relativelythinner fabric and as shown comprises a simple weave with wefts 13 andwarps 14. The manner of construction of this fabric layer is describedbelow. In the region of the seam 2 both the second fabric 4, and thebatt 5 are cut at the line 16 (the batt 6 if used is also cut at theline 17) to provide a flap 15. In use, the press felt moves in thedirection A, so that the flap 15 is downstream from the line of the seampintle 10.

In FIG. 2 is shown a part sectioned view of the paper side layer face ofthe fabric in FIG. 1. The paper side face proper is the layer of batt 5.The batt layer 5 overlays the second fabric 4, which is located on thepaper side of the first layer 3. The first layer 3 is woven to be thefull width of the press felt, whilst the second layer is woven as a muchnarrower strip, so that the two distances X and Y both of which are moreor less in the cross machine direction are different, with Y beinglarger than X. The narrower second layer is also applied over the firstwith a lateral edge 4A at a cant angle θ to the machine directionindicated at 4B, which is also substantially parallel to the edge of thepress felt. The second layer is applied using essentially the techniquesdescribed by Best et al. in U.S. Pat. No. 5,268,076 and by Rexfelt etal. in U.S. Pat. No. 5,360,656, the disclosures of which areincorporated herein by reference.

The fabric of FIG. 2 is assembled as follows. As the first step thefirst layer of fabric is woven to a suitable double layer design basedon the conditions obtaining in the press section in which the press feltis to be used. It can be woven flat, or woven as a continuous run, whichlatter is preferred. A suitable length of this fabric is then taken andthe pin seam 2 created in it to provide a continuous seamed loop 3 ofthe required length. The second layer 4 is then wound onto the firstwith a lateral edge 4A at the desired cant angle θ to the machinedirection 4B, using essentially the techniques described by Best et al.in U.S. Pat. No. 5,268,076 and by Rexfelt et al. in U.S. Pat. No.5,360,656. The paper side batt layer 5 is then applied either usingconventional techniques, or to obtain a desired batt orientation usingthe method described by Kr{hacek over (o)}ma et al., in a paper titled“Perpendicular Laid Bulky Nonwovens”, 7th World Conference of TheTextile Institute, Atlanta, Ga., USA, September 1994, which isincorporated herein by reference. After the batt has been applied, thebatt 5 and the second fabric layer 4 are both cut at 16 on the correctdownstream side of the line of the pintle so that the seam can beseparated to allow installation into the press section, and to providethe flap 15.

An alternative fabric is shown in FIG. 3. This fabric is similar to thatshown in FIGS. 1 and 2, and is constructed by the same techniques. Thefabric as shown has a paper side batt layer 5, and beneath it a secondlayer 4 which is wound onto a first layer 3. In addition, a third layer20 of the same general type as the second layer 4 is also provided onthe machine side of the first layer 3. The widths X₁ and X₂ of thestrips used in the first second and third layers 4 and 20 need not bethe same. However these two widths desirably should be chosen to avoid acircumstance where a line of edge contact in the second layer is alignedwith and directly above a line of edge contact in the third layer,because any gap in the edge contact in either layer could cause markingof the paper. The second layer 4 is wound at a first cant angle θ₁,between the lateral edge 4A and the machine direction indicated at 4B,and the third layer 20 is wound at a cant angle θ₂ between the lateraledge 20A and the machine direction indicated at 20B. The first andsecond cant angles need not be the same, and need not be in the samesense relative to the machine direction.

The importance of the combination of using a relatively narrow strip forthe second layer, or for the second and third layers, which has alateral edge at a cant angle θ to the machine direction is that when thesecond fabric is cut to open the seam at any given point there is only ashort length of second, and, when used, third, fabric yarn which canunravel when the press fabric is in use. The amount which can unravel islimited by the width X of the narrow strip of the layer, and the valueof the cant angle θ.

In experimental fabrics it has been found that cant angles as low as1.7° (which corresponds to an angle of 3 cm per meter) can be usedsuccessfully, up to a maximum angle of about 20° above which the risk ofunraveling again appears to become a problem. It appears that a cantangle of less than about 10° is desirable.

The relative widths of the first layer and the strips used for thesecond and third layers, as appropriate, is at least in part determinedby the width of the press section. The strips have to be of adequatewidth to be woven, and should be significantly narrower than the firstlayer, since if they are made too wide the amount of yarn that canunravel increases. It appears that a ratio of at least 2:1 is desirable.However for a wide press section it is not possible to maintain such alow ratio, and ratios up to at least about 20:1 appear to be useable. Itis also possible to use different width strips when both a second and athird layer are used.

The choice of fabric weave used for each of the layers is open toconsiderable flexibility, and will mainly be determined by the proposedconditions of use. As a generality, the first layer should be a doublelayer fabric, mainly to facilitate construction of the pin seam. Thesecond, and where used, third, layer is generally a single layer fabric,and is preferably a different weave in terms of yarns count/cm than thefirst layer. It can be either a finer weave or a coarser weave, and insome applications a second, or third, layer that is a double layerfabric might be used. The second and third layer fabrics also need notbe the same. Furthermore, these fabrics need not be woven ones, and aknitted fabric strip can be used in certain applications.

1. A multilayer papermaker's press felt fabric comprising incombination: a woven first fabric layer incorporating therein a crossmachine direction pin seam, a second fabric layer on the paper side faceof the first fabric layer, a layer of needled batt applied to the paperside face of the second layer which penetrates into the first fabriclayer thereby binding the first and second layer together, and a flapcomprising a short length of the second fabric layer with attached battoverlaying the pin seam in the first layer, wherein: (a) the secondlayer comprises a plurality of relatively narrow strips, and (b) thestrips of the second layer are located with a lateral edge at a firstcant angle to the machine direction, and (c) the first cant angle has avalue of from more than 1° to less than 20°.
 2. A fabric according toclaim 1 further including a third layer on the machine side of the firstlayer wherein: (a) the third layer comprises a plurality or relativelynarrow strips, and (b) the strips of the third layer are located with alateral edge at a second cant angle to the machine direction, and (c)the second cant angle has a value of from more than 1° to less than 20°.3. A fabric according to claim 1 wherein the first cant angle has avalue of from more than 1° to less than 10°.
 4. A fabric according toclaim 2 wherein the first cant angle for the second fabric layer has avalue of from more than 1° to less than 10°.
 5. A fabric according toclaim 1 wherein the second cant angle for the third fabric layer has avalue of from more than 1° to less than 10°.
 6. A fabric according toclaim 2 wherein the cant angles of the second and third fabric layersare the same.
 7. A fabric according to claim 2 wherein the cant anglesof the second and third fabric layers are not the same.
 8. A fabricaccording to claim 2 wherein the cant angles of the second and thirdfabric layers are in the same sense relative to the machine direction.9. A fabric according to claim 2 wherein the cant angles of the secondand third fabric layers are not in the same sense relative to themachine direction.
 10. A fabric according to claim 1 wherein the ratioof the widths of the first and second layers layer and the strips of thesecond layer is at least 2:1.
 11. A fabric according to claim 2 whereinthe ratio of the widths of the first and second layers layer and thestrips of the second layer is at least 2:1.
 12. A fabric according toclaim 2 wherein the ratio of the widths of the first and third layerslayer and the strips of the third layer is at least 2:1.
 13. A fabricaccording to claim 2 wherein the widths of the second and third layersare the same.
 14. A fabric according to claim 2 wherein the widths ofthe second and third layers are not the same.
 15. A fabric according toclaim 1 wherein the batt is oriented in a desired direction.
 16. Afabric according to claim 1 wherein the second fabric layer is of wovenor knitted construction.
 17. A fabric according to claim 2 wherein thebatt is oriented in a desired direction.
 18. A fabric according to claim2 wherein the second fabric layer is of woven or knitted construction.19. A fabric according to claim 2 wherein the third fabric layer is ofwoven or knitted construction.
 20. A fabric according to claim 1 whereinthe first layer is woven as a double layer fabric.
 21. A fabricaccording to claim 2 wherein the first layer is woven as a double layerfabric.
 22. A fabric according to claim 1 wherein the ratio of thewidths of the first and second layers layer and the strips of the secondlayer is from at least 2:1 to 20:1.
 23. A fabric according to claim 2wherein the ratio of the widths of the first and second layers layer andthe strips of the second layer is from at least 2:1 to 20:1.
 24. Afabric according to claim 2 wherein the ratio of the widths of the firstand third layers layer and the strips of the third layer is from atleast 2:1 to 20:1.